The present invention relates to the field of optics and specifically to the field of optical metrology, and more precisely to the measurement of the various parameters needed to produce spectacles. In the production of spectacles, it is necessary to cut the lenses designed to be fitted into the frame as a function of the choice of frame and of various parameters linked to the spectacle wearer. These parameters include the distance between the pupils or in other words the horizontal distance between the eyes of the spectacle wearer, and various heights or distances with respect to the pupil of each eye.
Various optical metrology methods are known. Conventionally, the optician directly measures the various parameters on the spectacle wearer, using a measuring instrument. This method is not very accurate. Another disadvantage is that the measurements are not taken in the natural position for the spectacle wearer, but rather at a position for which the spectacle wearer is somewhat constrained, with his head being kept at a fixed position, various measuring devices being present in the visual field, etc.
To overcome these disadvantages, in French Patent Application 2,690,832 an image of the face of the wearer carrying a frame is captured by means of a digitizing device, the various parameters then being measured on this image. It is suggested there that this image be displayed on a screen. Following this, the optician uses a mouse pointing device to locate the extreme upper and lower, and lateral, points of the frame on the screen to thereby trace a rectangular framework tangential to the frame, on the screen. A comparison between the dimensions of this framework and the theoretical shape of the frame obtained by other means, enables the image to be scaled to a known size. Following this, the position of the pupil of each eye is marked on the image, in order to calculate the various parameters.
A similar method is implemented in a device known as the Video-Infral marketed by the Carl Zeiss company. Using two video cameras and a mirror, front and side views are obtained of the spectacle wearer. The optician then uses a mouse pointing device to trace, on these images, the tangents to the frame, and then moves the cursor or the mouse in order to determine the position of the center of the eye. The position of the patient's pupils with respect to the frame is then measured on the front view of the wearer, and the inclination of the frame with respect to the vertical is located on the side view image.
In both procedures, the optician is required to trace various points of the frame with the mouse, and to visually ensure the tangents are parallel. This renders these procedures time-consuming in practice. Moreover, the line drawing operations reduce the accuracy of measurement; evaluation of tangency between the frameworks and the spectacle frame depends on the person operating the device. It is difficult for these procedures to furnish reproducible results when successive measurements are taken.
In a device marketed by Rodenstock under the name Videocom, is proposed to employ a simple video camera to obtain an image of the person wearing the frame after a millimetric scaled accessory has been fitted onto said frame. Measurement is then done by clicking at the desired points of the image on the screen. Measurement in this device thus lacks accuracy.